A nonaqueous secondary battery basically comprises an anode active material, an electrolyte and a cathode active material comprising a lithium metal or a lithium alloy. In the secondary battery using lithium metal as the anode active material, highly active tree-like lithium metal (dendrite) or mossy lithium metal (moss) is formed on the anode during repetition of charging and discharging. When the dendrite or the moss peels off to become in contact with the cathode active material of the battery or when it grows to touch the cathode active material directly, an inner short circuit is produced within the battery.
Recently, as the battery using no lithium metal, proposed are some batteries using carbonaceous materials in which lithium metal or lithium ion can be intercalated and then deintercalated. Such batteries using carbonaceous materials generally have an advantage of increased discharge capacity. Even in the battery, however, lithium metal is deposited and the dendrite is formed on the carbonaceous material when the battery is overcharged or rapidly-charged because the carbonaceous material itself is an electric conductor. Therefore, the amount of the cathode active material is usually lowered so as to prevent the battery from overcharging. In such battery, however, the discharge capacity is not satisfactorily increased due to the restriction of the amount of the active material. Further, since the density of the carbon material is relatively low, its capacity per volume is small. Consequently, the charging-discharging capacity of the battery using such carbonaceous material is restricted for the above two reasons; the restrictions of the amount of the active material and the small capacity per volume.
On the other hand, as known examples of the anode active material other than lithium metal, alloy thereof and carbonaceous material, there can be mentioned TiS.sub.2 in which lithium ion can be intercalated and deintercalated, LiTiS.sub.2 (U.S. Pat. No. 3,983,476), WO.sub.2 having a rutile structure (U.S. Pat. No. 4,198,476), spinel compounds such as Li.sub.x Fe (Fe.sub.2)O.sub.4 and Li.sub.x MnO.sub.4 (U.S. Pat. No. 4,507,371), lithium compounds of electrochemically-synthesized Fe.sub.2 O.sub.3 (U.S. Pat. No. 4,464,447), lithium compounds of Fe.sub.2 O.sub.3 (Japanese Patent Provisional Publication No. 3 (1991)-112070), Nb.sub.2 O.sub.5 (Japanese Patent Publication No. 62(1987)-59412 and Japanese Patent Provisional Publication No. 2(1990)-82447), iron oxides such as FeO, Fe.sub.2 O.sub.3 and Fe.sub.3 O.sub.4, and cobalt oxides such as CoO, Co.sub.2 O.sub.3 and Co.sub.3 O.sub.4 (Japanese Patent Provisional Publication No. 3(19901)-291862). However, each of these known compounds has too high redox potential to give a nonaqueous secondary battery having high discharge potential of 3 V or higher and high discharge capacity.
As known combinations of the metal chalcogenide cathode active material and the metal chalcogenide anode active material, there can be mentioned TiS.sub.2 and LiTiS.sub.2 (U.S. Pat. No. 983,476), chemically synthesized Li.sub.0.1 V.sub.2 O.sub.5 and LiMn.sub.1-s Me.sub.s O.sub.2 (0.1&lt;s&lt;1, Me: transition metal, Japanese Patent Provisional Publication No. 63 (1988)-210028); chemically synthesized Li.sub.0.1 V.sub.2 O.sub.5 and LiCo.sub.1-s Fe.sub.s O.sub.2 (s=0.05-0.3, Japanese Patent Provisional Publication No. 63(1988)-211564), chemically synthesized Li.sub.0.1 V.sub.2 O.sub.5 and LiCo.sub.1-s Ni.sub.s O.sub.2 (s=0.5-0.9, Japanese Patent Provisional Publication No. 1(1989)-294364); V.sub.2 O.sub.5 and Nb.sub.2 O.sub.5 +lithium metal (Japanese Patent Provisional Publication No. 2(1990)-82447), V.sub.2 O.sub.5 or TiS.sub.2 and electrochemically synthesized Li.sub.x Fe.sub.2 O.sub.3 ((U.S. Pat. No. 4,464,447; Journal of Power Sources vol.8(1982) pp.289); LiNi.sub.x Co.sub.1-x O.sub.2 for both of cathode and anode active materials (0.ltoreq.x&lt;1, Japanese Patent Provisional Publication No. 1(1989)-120765; according to the example of this specification, the same compound was used for both of cathode and anode active materials); and LiCoO.sub.2 or LiMn.sub.2 O.sub.4 (for cathode) and iron oxides such as FeO, Fe.sub.2 O.sub.3 and Fe.sub.3 O.sub.4, or cobalt oxides such as CoO, Co.sub.2 O.sub.3 and Co.sub.3 O.sub.4 (for anode) (Japanese Patent Provisional Publication No. 3(1991)- 291862).
However, any of these combinations can not give a lithium secondary battery which has high capacity and high discharge potential of 3 V or higher.
In the above-mentioned Li.sub.x Fe.sub.2 O.sub.3 (Journal of Power Sources vol.8(1982) pp.289) which is used as the anode active material after electrochemical insertion of lithium ions, its X-ray diffractogram is changed by insertion of lithium ions and the diffractogram is further changed after discharging. Therefore, the charging-discharge capacity is lowered during repeated charging and discharging, charge-discharge cycle life is rendered short in addition to the low discharge potential. Further, in the above-mentioned spinel compound such as Li.sub.x Fe(Fe.sub.2)O.sub.4 or Li.sub.x MnO.sub.4 (U.S. Pat. No. 4,507,371) which is also used as the anode active material by electrochemical insertion of lithium ions thereinto, the required insertion is carried out so as not to destroy the spinel structure of the compound, and repeated charging and discharging are performed keeping the spinel structure. The reason resides in that the compound does not serve as an active material of a secondary battery if the spinel structure is destroyed due to insertion of an excessive amount of lithium ions and repetition of charging-discharging.
As is described above, a compound that is scarcely changed in the crystalline structure during repetition of charging and discharging and that there is little restrict in the insertion amount of lithium ions, is preferred as an anode active material. Hence, such compound is desired to produce a nonaqueous secondary battery having a high discharge potential and high discharge capacity and showing little the lowering of the discharge capacity during repeated charging and discharging.